There are numerous instances in the analysis of complex mixtures where it is desirable, indeed even necessary, to isolate and determine the structure of various individual components of the mixture. For example, in pyrolytic analysis or thermal extraction techniques, materials such as polymers and other organic and inorganic solids are subjected to high temperatures to thermally degrade and/or effect separation of components of the material. It will be appreciated that in such techniques, a myriad of various products may be produced or evolved. In order for these analysis techniques to be meaningful, it is necessary that the evolved products be identified so that conclusions can be reached regarding the structure of the sample subjected to analysis, the mechanism of decomposition, etc. An emerging use of pyrolytic analysis or thermal extraction techniques is in the environmental field where it is frequently necessary to subject solid samples to analysis to determine contaminating constituents. For example, soil samples contaminated with organic materials that may be toxic can be subjected to thermal extraction to thermal separate the organic components from the soil. Clearly, identification of the evolved components is of the utmost importance.
It is common practice in the field of instrumental analysis, e.g., gas chromatography, mass spectrometry, etc. to separate a complex mixture of compounds into individual components by passing the components through a chromatographic column using a carrier or sweep gas. Typically, although not always, the chromatographic column will contain a substrate the exhibits different affinities for the individual components. Accordingly, as the individual components are carried through the column by the carrier gas, they are more or less retained or held up by the substrate depending upon their affinity for the substrate with the net result that the components are separated and elute, ideally individually, from the column.
One problem in the separation of components is that very light, normally gaseous components, e.g., C.sub.1 -C.sub.4 hydrocarbons, produced as a result of thermal extraction and/or pyrolytic analysis, do not evolve as a single peak from the sample being analyzed. Consequently, as they are evolved in the thermal extraction technique, they tend to be swept through the separating column without much separation with the result that no discernible peak is observed. Accordingly, it is not possible to identify these highly volatile components.
To solve this problem, it is known to trap the lower boiling components prior to their entering the separation or chromatographic column so that instead of slowly bleeding through the chromatographic column, the entire trapped sample can be injected, virtually instantaneously, into the column so that separation of the individual components of the low boiling mixture can be achieved, each component giving a well-defined peak. To accomplish this, it is necessary to have a trapping apparatus that can be rapidly converted from a high temperature to a very low temperature and then back to a high temperature again.
For example, a trap can consist of a section of tubing through which the carrier gas containing the components flows, the section of the tubing being immersed in liquid nitrogen or some other such cooling medium that will effectively solidify (freeze) the components and cause them to be removed from the carrier gas. It must be remembered that, typically, the carrier gas and the components therein are at elevated temperatures to prevent certain components from condensing out in the column. Once components have been trapped, it is then necessary to revaporize them so that they can be removed from the trap and directed into the chromatographic column for separation. It is also desirable for speed of analysis that it be possible to rapidly raise the temperature of the trapped (frozen) components so that they can be vaporized from the trap rapidly.
Prior art traps of the type described above are generally cumbersome, multipart devices that do not readily lend themselves to easy trapping of a sample by freezing and then rapid vaporization of the trapped sample when desired.